Much of the thrust behind the growing fossil fuel divestment movement is the idea that it's a moral imperative and a matter of mission integrity. But there’s also an argument that such shifts will yield higher investment returns. If that case sticks, it might be just what it takes to move massive targets like the Gates Foundation.

The fossil fuel divestment movement is on a roll lately, piling up small-to-mid-sized colleges, churches, municipalities and foundations. While big foundations are still resisting, we’ve even seen a shift in policy for Hewlett Foundation, which has quietly elected to “refrain from future investments in private partnerships primarily involved in oil and gas drilling.” Getting there.

But there are some white whales in the campaign to get organizations to cut loose their investments in fossil fuel companies—those organizations so big that their enlistment would mark a seismic shift. On the foundation front, those targets are the Gates Foundation and the U.K.’s Wellcome Trust, with combined assets equivalent to around $70 billion.

The two foundations have resisted the concept of divestment. While they acknowledge the importance of combating climate change (both are primarily devoted to health) they don’t accept divestment as the right approach to doing so, or something that serves their missions. Much of the reluctance to divestment is that it would undermine financial stability.

And yet, there are signs, at least in the short term, that doing so would be financially smart—with Gates even making big changes to its stock holdings without fanfare. These trends could be what it really takes to get such outfits to budge.

We’ve written about the divestment movement since the early days, predicting that this is something that will eventually be accepted convention, much like the common practice of screening out investments in tobacco. But a big part of our reasoning, and a big argument the campaign has made, is roughly that organizations with missions for improving the world can’t publicly buy into an industry that is hurting it.

There’s also a somewhat philosophical argument about fossil fuel stock value. If the product in question can’t be accessed and burned without causing catastrophic damage, in reality, the stocks are actually worthless.

The argument that fossil fuels are simply a bad investment may be panning out sooner than later. The Guardian recently reported on analysis of the holdings of 14 major investment funds, most of which would have made more money had they replaced fossil fuel investments with those in green companies back in 2012. Gates, in particular, would have $1.9 billion more in the bank, the report found. (The Guardian is running a divestment campaign that focuses on Gates and Wellcome.)

Even more interesting is a recent analysis by the Seattle Times of Gates’ latest tax filings, which found that the foundation is, in fact, ditching investments in fossil fuel companies. The trust that handles Gates’ investments dropped holdings in such companies from $1.4 billion in 2013 to $475 million in 2014.

This raises a few new questions in the divestment saga.

First, are we talking about some kind of blip in the markets or an omen of a future economic reality? An economist in the Times story pointed out there are likely lots of investment funds dropping energy investments right now, but that's because of a short-term drop in oil prices and stock value. But maybe it's the start of a rocky road ahead for the oil and gas industry, as activists predict.

Second, is the Gates Foundation backing away from its fossil fuel stocks for purely economic reasons, or is there some element of response to public pressure or sense of moral obligation?

Maybe it's a little from column A and a little from column B. Campaigners for divestment would no doubt prefer a public proclamation and ideological statement of support. But whether these shifts are principled or practical, short term or long term, they're adding volume to the drumbeat that the fossil fuel industry is a sinking ship—kind of like real estate in Miami Beach.

Stephen Heintz, president of the Rockefeller Brothers Fund, invoked the long-term picture when that foundation announced its historic divestment move last year. “John D. Rockefeller, the founder of Standard Oil, moved America out of whale oil and into petroleum,” said Heintz. “We are quite convinced that if he were alive today, as an astute businessman looking out to the future, he would be moving out of fossil fuels and investing in clean, renewable energy.”